The invention relates to a truck for a railway vehicle which comprises an adjustable frame having side members and two axles having shrunk-on wheels and journalled in axle boxes each connected to the frame through a primary suspension comprising a link having one end connected to the axle-box and the other end connected to a side member of the frame through a resilient swivel joint. Such trucks are for example the trucks X32 of the French CORAIL cars. The invention more particularly relates to means for mounting at least one of the axle-boxes so as to allow it a degree of freedom of substantially horizontal relative motion with respect to the frame.
Present railway technique has permitted the development of railway trucks having wheels shrunk on the axle spindles which conserve good characteristics of stability up to speeds of 400 km/h and even beyond. Such trucks are based on the principle of a double suspension: a primary suspension and a secondary suspension, these two suspensions being separated by an intermediate movable element between the axles and the body of the vehicle designated truck frame.
It is known that the motions of instability at high speed (or biconical motions of undamped axles) can be suppressed in particular by high primary stiffnesses of the primary suspension considered in the horizontal plane.
Unfortunately, the stiffening of the horizontal flexible connections which maintain the axle-boxes relative to the truck frame has resulted in the concerned trucks badly taking the curves, i.e. the axles become decentered relative to the two rail lines and the wheel flanges come to abut against the outer rail of the curve, especially the wheel of the front axle of each truck.
A drawback of this phenomenon is that the contact of the wheel flanges results in both wear on the wheel flanges themselves and wear on the rolling surfaces of the wheels. A second drawback is that, in a curve, the axles effected by the contact between the flange and outer rail follows the defects on the inner rounded portion of the rail on which the contact occurs and the suspension transmits undesirable forces to the body.
The adoption of the greasing of the wheel flanges or the rails in a curve permits combatting the first drawback but not the second. A concern of designers is therefore to propose a solution for correctly positioning the axles with respect to the track, even in a curved track, with the centers of the axle-boxes located at the four corners of a rectangle.
Thus, in order to improve the passage through a curve a certain number of specialists have proposed mechanical link systems employing the relative rotational motion of the equipment constituted by the two axles of a truck (or even of each axle of rolling stock with merely axles) relative to the body placed vertically thereabove. These link systems have the purpose of modifying the relative disposition of the axle-boxes with respect to one another as a function of the curve radius so as to obtain in a curve a truck geometry which is more favorable to its taking the curve.
But the systems proposed at present above all aim to create in an established curve a geometry favorable to the truck considered in the free state, i.e. without taking into account semi-slip forces which occur in the contact between the wheels and the rails.
In a certain number of proposed solutions, the position of equilibrium cannot be attained, even if the geometry of the wheels obtained in a curve by a "forced" motion corresponds to a truck which takes the considered curve well, quite simply because the proposed truck is not morphologically designed for an automatic seeking of a correct positioning of the axles with respect to the track. Thus, for example, it is not sufficient to make the axes of two axles of a truck converge in the correct direction for them to make an angle equal to the angle at the center from which is seen, from the center of the considered curve, a segment equal to the wheelbase of the truck so that this truck behaves well in the considered curve. In failing to take certain constructional precautions, the detail of which constitutes a characteristic of the present invention and will be explained hereinafter, there is a risk that a truck according to the aforementioned example will place itself across the curved track and advance crabwise.
There are, for example, known from the patent documents German DE-A-3 424 531 or European EP-A-165 752, trucks of the type mentioned at the beginning of this description, provided with means for mounting the axle-boxes adapted to enable the axles to assume in a curve a certain inclination relative to the longitudinal axis of the frame. But these means, arranged in parallel with the primary suspension, consist of linkages which fix in position at least two axle-boxes. The primary suspensions are necessarily rendered more flexible and the linkage exerts on the boxes high stresses transmitted by numerous link members which are fragile and liable to result in play, which is therefore unsatisfactory.